We present a comparison of Class ii CH3OH (6.7 GHz)
and H2O (22.2 GHz) masers at high spatial resolution in a sample
of 29 massive star-forming regions. Absolute positions of both maser
types are compared with mm dust continuum, cm continuum and
mid-infrared sources. All maser features – regardless of the
species – are associated with massive mm cores, but only 3 out of
18 CH3OH masers and 6 out of 22 H2O masers are associated with
cm emission likely indicating the presence of a recently ignited
massive star. These observations of a homogenous sample of massive,
young star-forming regions confirm earlier results, obtained for each
maser species separately, that both maser types are signposts of
high-mass star formation in very early evolutionary stages. The data
are consistent with models that explain CH3OH maser emission by
radiative pumping in moderately hot cores, requiring the absence, or
only weak, free-free cm continuum radiation due to recently ignited
stars. Mid-infrared sources are associated with both maser types in
approximately of the observed fields. Thus, mid-infrared
objects may power maser sites, but the detection of strong
mid-infrared emission is not strictly necessary because it might be
heavily extincted. A comparison of the spatial separations between
the different observed quantities and other properties of the
star-forming regions does not reveal any correlation. Our data
suggest that CH3OH and H2O masers need a similar environment
(dense and warm molecular gas), but that, due to the different
excitation processes (radiative pumping for CH3OH and collisional
pumping for H2O), no spatial correlations exist. Spatial
associations are probably coincidences due to insufficient angular
resolution and projection effects. The kinematic structures we find
in the different maser species show no recognizable pattern, and we
cannot draw firm conclusions as to whether the features are produced in
disks, outflows or expanding shock waves.

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.